The Biology of Polyporus Pargamenus Fries 97 
occasionally they may extend at right angles to them. At 
this stage they are quite empty of contents save for a few 
scattered tubular elements — the vessels. Owing to their 
greater lignification, these elements are the last to disappear 
under the dissolving action of the fungus. In time, however, 
even these disappear, leaving practically nothing within the 
pockets, which by this time are separated by almost mem- 
branous layers of woody tissue merely a few cells thick. 
(Plate XXIV, Fig. 1.) Numerous strands of white myce- 
hum, running both longitudinally and radially through the 
decayed wood, can be seen with the unaided eye. By the 
time the decay has progressed to this point, the wood has 
lost all of its original characteristics of color, odor, hardness, 
and strength, and has become a bleached mass of pithy 
consistency. 
Blocks of wood cut from a decayed log and kept in culture 
chambers decayed much more rapidly than they normally 
would under field conditions. In a few weeks they became 
covered with a growth of mycelium which thrived for several 
weeks. After that time the growth of the mycelium seemed 
to cease and portions of the mycelial mass died and became 
discolored. Portions of these blocks of decayed wood were 
even softer in texture than a wet sponge and the decay seemed 
to have progressed to its utmost extent since the mycelium 
within the woody tissue apparently was functioning no 
longer. The decayed wood appeared like a honeycomb com- 
posed of the finest and most delicate, whitish membranes. 
By this time the decayed pockets had fused together to such 
an extent that some were found to measure three mm. in 
diameter and to extend lengthwise through the wood for 
three cm. It may be assumed with reasonable certainty that 
the wood at this time was in the final stage of decomposition 
for we have no reason to think that w fads, tissue must be 
entirely destroyed in order that the specific decay be com- 
pleted. It is only natural to suppose that the growth of the 
mycelium will terminate when the nutrient substances have | 
been extracted reasonably thoroughly from the woody tissue. 
It is definitely known that wood-destroying fungi, owing to 
4. 
